This invention relates generally to conical cutters utilized in roller bits employed in the oil-well-drilling industry and in mining and, more particularly concerns unique combinations including materials, that make up the composite cone and a unique manufacturing process by which the said composite cones are formed. The description of the invention that follows relates to three-cone rolling cutter bits manufactured for the oil and gas industry; however, the invention is applicable to other types of bits utilizing conical rolling cutters, such as two-cone rolling cutter bits, geothermal and mining bits. Of primary importance from bit manufacturing and design points of view is the assurance that the bit will exhibit the desired cutting action, that it will leave no rings of uncut formation on the hole bottom, that it will be capable of drilling at an economically-acceptable rate of penetration (into the rock formation), and that the bearing and cutting structures are sufficiently durable so that the bit can achieve maximum drilling footage at its maximum rate of penetration. Among these, rate of penetration and structural durability to achieve drilling depths are the most important factors from the user's point of view and are related to the subject matter of this invention.
The invention is primarily concerned with the cutting elements which are integral with the cone structure, as opposed to carbide cutting elements which are fitted into holes drilled into the cone, as is the practice presently. As the bit is rotated, the cones roll around the bottom of the hole, each tooth intermittently penetrating into the rock, crushing, chipping and gouging it. The cones are designed so that the teeth intermesh, to facilitate cleaning. In soft rock formations, long, widely-spaced steel teeth are used which easily penetrate the formation.
The present state-of-the-art manufacturing methods usually involve forging, then machining, of the cone followed by hardfacing of the steel teeth. Hardfacing is applied in a way to provide not only a hard-wear resistant layer to reduce the rate at which the cutting elements (teeth) are worn off, but to provide a sharp cutting edge as the tooth wears. This manufacturing scheme, however, is heavily labor dependent, and imprecise in that hardfacing deposit thickness, as well as its chemical composition, is not normally uniform. This is a consequence of several factors which the conventional manufacturing methods cannot, in a practical and commercially-viable sense, control.
Consider first how the hardfacing operation is performed. A rod of the hard-wear resistant alloy is fed into a jet of hot welding arc or flame. Heat causes the rod to melt and deposit onto the steel tooth which also becomes hot and partially molten. Then, the deposit is allowed to solidify. Even if one assumes that the hardfacing alloy is introduced uniformly and the heat is applied uniformly, both of which are usually not achieved, the natural phenomena that determine the way the molten deposit freeezes, are not controlled. For example, the rate of removal of heat from the molten puddle is not uniform, because the steel tooth shape is not uniform. Consequently, tooth tips remain hot longer due to insufficient chilling action of the tooth section there, while at the root of the tooth, the massive steel cone body extracts heat quickly and solidification occurs rapidly. This can easily produce a deposit that is non-uniform in thickness and non-uniform in chemistry in a micro-structural sense. Additionally, gravity, surface tensional forces and environmental reactions, such as oxidation, play complicated roles in preventing the formation of a uniform structurally-sound hard-faced deposit.
One objective of the present invention is to provide a uniform and structurally-sound hard-wear resistant layer or layers at the desired locations on the cone, thus improving the cutting action of the conical cutters and allowing longer drilling times at maximum rates of penetration.
Another objective of the invention is to reduce the labor content of the drill bit cone by utilizing a high-temperature/short-cycle consolidation process by which a compositely-structured cone can be produced from its powders or powder plus solid components combinations.
A further objective is to increase the freedom of material selection for the various components of the cone as a direct result of the use of a short-time/high-temperature consolidation process which does not affect the useful properties of the cone and its components. Thus, materials and material combinations heretofore not used in conical cutters of steel tooth design, may be used without fear of detrimental side effects associated with long-time/high temperature processing operations.